Control valve for shock absorbers

ABSTRACT

A direct acting shock absorber for damping the movement of the body of an automobile is disclosed. The shock absorber comprises a pressure cylinder forming a working chamber having first and second portions operable to store damping fluid. A piston is disposed within the pressure cylinder between the first and second portions of the working chamber. The shock absorber further comprises a fluid reservoir operable to store damping fluid. The shock absorber also includes a valve for permitting damping fluid to flow from the first portion of the working chamber to the fluid reservoir during movement of the piston in a first direction. Finally, a second valve is provided for permitting damping fluid to flow from the fluid reservoir to the second portion of the working chamber during movement of the piston in a second direction.

CROSS-REFERENCE TO RELATED APPLICATION

This is a continuation of U.S. patent application Ser. No. 07/322,542,now U.S. Pat. No. 4,855,460, filed Mar. 13, 1989; which is acontinuation-in-part of Ser. No. 07/227,113, filed Aug. 1, 1988, nowabandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to vehicle suspension systems, and moreparticularly to a valve for controlling the internal fluid displacementin a shock absorber.

2. Description of the Related Art

Shock absorbers are used in connection with automobile suspensionsystems and other vehicle suspension systems to absorb unwantedvibrations which occur during locomotion. To absorb this unwantedvibration, shock absorbers are generally connected between the body andthe suspension of the automobile. A piston is located within the shockabsorber and is connected to the vehicle body through a piston rod.Because the piston is available to limit the flow of damping fluidwithin the working chamber of the shock absorber when the shock absorberis compressed or extended, the shock absorber is able to produce adamping force which counteracts the vibration which would otherwise betransmitted from the suspension of the automobile to the body.

A conventional shock absorber comprises a pressure tube with a pistontherein and a reserve tube surrounding the pressure tube. A piston rodconnected to the piston projects from one end of the pressure tube. Atthe other end of the pressure tube is a valve communicating with thereserve tube Damping is controlled by orifices in the piston whichregulate passage of fluid from one side of the piston to the other Dueto the presence of a piston rod on only one side of the piston,different volumes of hydraulic fluid must be displaced on thecompression and rebound strokes. This difference is the rod volume.

The rod volume of hydraulic fluid is pushed out of the pressure tubeduring the compression stroke through the valve in the base of the shockabsorber. The hydraulic fluid is then stored in the reserve tube whichsurrounds the pressure tube of the shock absorber.

During the rebound stroke, this fluid which was displaced into thereserve tube through the base valve reenters the pressure tube via thesame valve. As the piston moves back and forth within the pressure tube,the rod volume of oil is correspondingly pushed into and out of thereserve tube through the base valve. Thus only a portion of the fluid inthe reserve tube is effectively utilized. The remainder remainsrelatively static within the reserve tube. This quick exchange of fluidas well as the friction between the piston and tube wall generates heatwhich is very undesirable during prolonged operating conditions. Becauseof the cyclic fluid exchange through the base valve, the generated heatis concentrated near the base of the pressure tube. The generation ofthis heat decreases the viscosity of the hydraulic fluid and decreasesthe lifetime of the operability of the shock absorber.

In addition, because conventional shock absorbers use a base valve, thedamping forces generated during compression could not be completelycontrolled by the amount of damping fluid flowing through the piston.Because the damping forces could not be completely controlled by theamount of damping fluid flowing through the piston, the range of dampingwhich adjustable damping suspension systems could provide was oftensomewhat limited.

SUMMARY OF THE INVENTION

Accordingly, it is a primary object of the present invention to providea shock absorber in which the amount of damping forces generated duringcompression is independent of the operation of the base valve.

Another object of the present invention is to provide a shock absorberthat circulates the rod volume of hydraulic fluid into the reserve tubeso as to provide an increased heat sink capability of the shockabsorber.

A further object of the present invention is to provide a shock absorberhaving improved operational life due to operation at lower working fluidtemperatures.

A shock absorber according to the present invention, has a control valvearranged at the upper end of the pressure tube in addition to the basevalve at the bottom of the pressure tube. According to the principal ofthe present invention, during the compression stroke of the shockabsorber piston, the rod volume of hydraulic fluid is discharged out ofthe pressure tube through the valve at the upper end of the pressuretube and into the outer reserve tube. During rebound, or extension, therod volume of hydraulic fluid is replaced from the bottom of the reservetube through the base valve into the lower portion of the pressure tube.In the present invention, therefore, hydraulic fluid that is pushed outof the pressure tube into the reserve tube enters the reserve tube atthe top. This hydraulic fluid must then travel the entire length of thereserve tube prior to returning into the pressure tube via the basevalve.

Thus the present invention sets up a single flow path and direction intoand out of the reserve tube. Entering fluid must travel the length ofthe reserve tube prior to returning to the pressure tube. This prolongsthe period of time in which a given body of oil resides in the reservetube, thus greatly enhancing the heat dissipation capability of theshock absorber. Consequently, the shock absorber operates at a lowertemperature which in turn prolongs shock absorber life.

BRIEF DESCRIPTION OF THE DRAWINGS

Various advantages of the present invention will become apparent to oneskilled in the art upon reading the following detailed description andby reference to the following drawings in which:

FIG. 1 is a schematic representation of the shock absorbers, accordingto the present invention, in operative association with a typicalautomobile;

FIG. 2 is a side elevational view, partially broken away of one of theshock absorbers according to the present invention shown in FIG. 1;

FIG. 3 is an enlarged side elevational view of the upper portion of theshock absorber shown in FIG. 2, with portions partially broken awayshowing the valve arrangement of one preferred embodiment of the presentinvention;

FIG. 4 is an enlarged view of a portion of FIG. 3;

FIG. 5 is an enlarged view of a second preferred embodiment of theinvention shown in FIG. 3 having an additional fluid reservoir at theupper end of the pressure tube;

FIG. 6 is an enlarged view of a third alternative preferred embodimentof the invention shown in FIG. 3 having a raised valve seat and aplastic bushing between the rod guide and the rod;

FIG. 7 is a fourth alternative preferred embodiment of the presentinvention;

FIG. 8 is a fifth embodiment of the present invention;

FIG. 9 is a sixth embodiment of the present invention;

FIG. 10 is a seventh embodiment of the present invention; and

FIGS. 11 and 12 are an eighth embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, a plurality of four shock absorbers 10 according toa preferred embodiment of the present invention are shown. The shockabsorbers 10 are depicted in operative association with a diagrammaticrepresentation of a conventional automobile 12 having a vehicle body 14.The automobile 12 includes a rear suspension system 16 having atransversely extending rear axle assembly (not shown) adapted tooperatively support the vehicle's rear wheels 18. The rear axle assemblyis operatively connected to the automobile 12 by a pair of shockabsorbers 10 and a pair of helical coil springs 20. Similarly, theautomobile 12 has a front suspension system 22 including a transverselyextending front axle assembly (not shown) to operatively support thevehicle's front wheels 24. The front axle assembly is operativelyconnected to the vehicle body 14 by means of a second pair of shockabsorbers 10 and by another pair of helical coil springs 20. The shockabsorbers 10 serve to damp the relative movement of the unsprung portion(i.e., the front and rear suspension systems 22 and 16) and the sprungportion (i.e., the body 14) of the automobile 12. While the automobile12 has been depicted as a passenger car, the shock absorber 10 may beused with other types of vehicles or in other types of vibration dampingapplications. Further, the term "shock absorber" as used herein willrefer to shock absorbers in the general sense of the phrase and willinclude MacPherson struts.

With particular reference now to FIG. 2, the shock absorber 10 accordingto the present invention is shown. The shock absorber 10 comprises anelongated pressure tube cylinder 30 defining a damping fluid containingworking chamber 32. A slidably movable piston 34 divides chamber 32 intoand defines a lower first portion 36 and an upper second portion 38. Thereciprocal piston 34 is secured to one end of an axially extendingpiston post 40 which is in turn secured to an axially extending pistonrod 42 which passes axially through upper portion 38.

The piston 34 comprises a housing 44, shown in FIG. 3, having aplurality of ridges 46 disposed on the annular exterior of the pistonhousing 44. The ridges 46 are used to secure an annular teflon sleeve 48which is disposed between the ridges 46 of the piston housing 44 and thepressure cylinder tube 30. The teflon sleeve 48 permits movement of thepiston 34 with respect to the cylinder 30 without generating unduefrictional forces.

Upward movement of the piston 34 is limited by a radially extending stepportion 50 of the piston post 40. Downward movement of the piston 34 islimited by a threaded nut 52 or similar type fastening element which isthreadably received upon the lower portion 54 of the piston post 40. Ahelical coil spring 56 is arranged concentrically of the nut 52 and issupported at the lower end thereof by a radially outwardly extendingflange 58 on the lower end of the nut 52. The upper end of the spring 56bears against a spring retainer 60 which in turn acts against a valvedisk 61 and the underside of the housing 44 to thereby resiliently urgethe piston upward. The piston 34 including valve disks 61 provides ameans for controlling the flow of damping fluid between the first andsecond portions 36 and 38 of the working chamber 32 through a pluralityof orifices 62 in piston housing 44.

It is to be understood that the piston 34 is described in general termsas the present invention may be used with a wide variety of pistondesigns. One such piston is disclosed in U.S. Pat. No. 4,113,072, whichis hereby incorporated by reference.

The shock absorber 10 further comprises a base valve 63 located withinthe lower end of the pressure cylinder 30 which is used to permit theflow of damping fluid into the working chamber 32 from an annular fluidreservoir 64 during rebound. The annular fluid reservoir 64 is definedas the space between the outer periphery of the cylinder 30 and theinner periphery of a reservoir tube or cylinder 66 which is arrangedpreferably concentrically around the exterior of the pressure cylinder30. The base valve 63 may be designed so that damping fluid is unable toflow through the base valve 63 during compression. If the base valve 63is designed in this manner, the damping forces generated duringcompression will be substantially fully controlled by the amount ofdamping fluid flowing through the piston 34. Accordingly, the range ofdamping which may be generated by the shock absorber 10 may be somewhatlarger than otherwise possible if the shock absorber 10 is part of anadjustable damping suspension system.

The lower end of the shock absorber 10 is provided with a cup-shapedlower end cap 68 closing the lower end of the reservoir tube 66. Theupper end of the shock absorber 10 includes a generally cup-shaped endcap 70 having an aperture therethrough for passage of piston rod 42. Theupper portion (not shown) of the piston rod 42 is attached to thevehicle body 14 in a conventional manner. A suitable end fitting 72 issecured to the lower end of the lower end cap 68 for operativelysecuring the shock absorber 10 to the axle assembly of the automobile 12also in a conventional manner.

Referring now to FIG. 3 and to the enlarged upper portion of the shockabsorber 10 shown in FIG. 4, a control valve arrangement according to afirst preferred embodiment of the present invention is shown. Inside theupper end cap 70 at the upper end of pressure tube 30 is a rubber orplastic annular seal 100. The seal 100 is adjacent to the periphery ofthe piston rod 42 and is used to prevent dirt and foreign matter fromentering the working interior of the shock absorber 10. The seal 100 isretained in position by a seal retainer 102 and the end cap 70 and formsone boundary of a first annular cavity 104 between the seal retainer102, the piston rod 42 and the seal 100. Between annular cavity 104reservoir 64 is a flow passage 106. The flow passage 106 allows dampingfluid to flow through the seal retainer 102 between the cavity 104 andthe reservoir 64. The operation of the flow passage 106 will be morefully described below.

An annular rod guide 108 having an upper section 110 and a lower section212 is positioned adjacent to the periphery of the piston rod 42 belowthe seal retainer 102. The upper section 110 of the annular rod guide108 abuts the seal retainer 102, while the lower section 112 of theannular rod guide 108 is fitted within the pressure tube 30 The annularrod guide 108 provides radial support to the piston rod 42 whileallowing axial movement of the piston rod 42 within the pressure tubecylinder 30.

The upper section 110 of the annular rod guide 108 has an insidediameter greater than the inside diameter of the lower section 112 ofthe annular rod guide 108 thereby forming a second annular cavity 114between the piston rod 42, the upper section 110 of annular rod guide108 and the seal retainer 102. A second axially extending flow passage116 is formed between the seal retainer 102 and the piston rod 42 whichallows fluid communication between the cavity 104 and the cavity 114.

Positioned within the annular cavity 114 and adjacent to the peripheryof the piston rod 42 is a frictional slip ring 118 The slip ring 118moves between contact with the seal retainer 102 when the piston rod 42moves in an upward direction, and contact with the annular rod guide 108when the piston rod 42 moves in a downward direction. As the piston rod42 continues upward or downward travel, the slip ring 118 slides alongthe surface of the annular piston rod 42 so that the slip ring 118remains in contact with either seal retainer 102 or rod guide 108,respectively

As can be seen in FIG. 4, when the annular piston rod 42 moves in anupward direction, the slip ring 118 moves into contact with the sealretainer 102 thereby preventing the flow of damping fluid through theflow passage 116. Because the slip ring 118 is able to slide along thesurface of the annular piston rod 42, further upward movement of thepiston rod 42 continues to maintain slip ring 118 in sealing engagementwith seal retainer 102. When the piston rod 42 is moved in a downwarddirection, the slip ring 118 is displaced from the seal retainer 102thereby allowing damping fluid to flow through the flow passage 116 fromthe first cavity 104 through the seal retainer 102 to the second cavity114.

The shock absorber 10 further comprises a cylindrical sleeve 120 whichis positioned concentric to and radially spaced outwardly from the uppersection 110 of the rod guide 108. The sleeve 120 is secured between theseal retainer 102 and the lower section 112 of the rod guide 108 to forma third annular cavity 122. The shock absorber further comprises anaxially aligned third flow passage 124 through lower section 112 of therod guide 108. The third flow passage 124 fluidly communicates betweenthe upper portion 36 of working chamber 32 and the third annular cavity122. A first orifice 126 disposed on the upper section 110 of the rodguide 108 allows fluid communication between the second cavity 114 andthe third cavity 122. A second orifice 128 disposed on the sleeve 120allows fluid communication between the third cavity 122 and thereservoir 64.

To control the flow of damping fluid through the flow passage 124, anannular valve disk 130 is provided. The annular valve disk 130 isradially displaced from the piston rod 42 between the annular rod guide108 and the cylindrical sleeve 120. The disk 130 is biased in a downwarddirection against the lower section 112 of the annular rod guide by ahelical spring 132. The helical spring 132 is disposed in the thirdcavity 122 and provides sufficient biasing force against the valve disk130 so as to prevent the flow of damping fluid through the third flowpassage 124 until such flow is desired.

An O-ring or similar sealing element 134 disposed above disk 130 withinthe cavity 122 transmits the force from the spring 132 to the annularvalve disk 130 to valve disk 130 against the flow passage 124. Inaddition, the O-ring 134 provides a seal between the upper section 110of the annular rod guide 108 and the cylindrical sleeve 120. Disposedbetween the helical spring 132 and the O-ring 134 is a retaining disk136. The retaining disk 136 is used to distribute the downwardlydirected spring force from the spring 132 evenly around the O-ring 134.

During the compression stroke of the shock absorber 10, the slip ring118 moves downward with the piston rod 42 in a direction away from theseal retainer 102 thereby opening the second passage 116. Travel offrictional slip ring 118 is terminated when the slip ring 118 contactsthe annular rod guide 108. As piston rod 42 continues to move downwardduring compression, the slip ring 118 remains stationary against thelower section 112 of the annular rod guide 108. When the piston rod 42moves upward during rebound, the slip ring 118 frictionally rides upwardon the piston rod 42 until the slip ring 118 contacts the retainer 102.The slip ring 118 then remains stationary against the retainer 102during further upward motion of the annular rod guide 108 therebypreventing the flow of damping fluid through the flow passage 116.

During downward travel of the piston rod 42, there is a higher pressurewithin the working chamber 32 than in the reservoir 64. This pressure istransmitted through the flow passage 124 to the underside of the valvedisk 130. Accordingly, the force acting on the upper side of the O-ring134 includes the force due to the pressure of the hydraulic fluid in thereservoir 64 in addition to the force exerted by the spring 132 which istransmitted through the retaining disk 136. As shown in FIG. 4,hydraulic fluid in the reservoir 64 is in fluid communication with thereservoir 64 through the first passage 106 and the first annular cavity104, through second flow passage 116 to the second cavity 114, throughthe first orifice 126 to the third cavity 122 and the O-ring 134.Accordingly, the pressure differential across the O-ring 134 permits thevalve disk 130 to raise, thereby allowing hydraulic fluid to pass fromthe chamber 32 through the passage 124 into the cavity 122, through thesecond orifice 128 in the sleeve 120 and into the reservoir 64. The basevalve 63 is closed during the compression stroke so that the hydraulicfluid beneath the piston 34 is able to flow through the piston orifices62 from portion 36 to portion 38 as piston rod 42 is moved downward incompression.

During the rebound stroke, the piston rod 42 is moved in an upwarddirection. The upward movement carries the slip ring 118 into contactwith seal retainer 102, thus closing the second flow passage 116. Whenthe second flow passage is closed in this manner, the flow path ofhydraulic fluid between the reservoir 64 and the upper side of theO-ring 134 is isolated. Accordingly, the fluid pressure above the O-ring134 in the third cavity 122 is at the same pressure as the hydraulicfluid in the Working chamber 32 beneath rod guide 108. Due to the factthat the area above the O-ring 134 is greater than the area beneath thevalve disk 130, and due to the spring force exerted by helical spring132 against the retaining disk 136, annular valve disk 130 maintainspassage 124 closed thus, closing off the orifice 128. Accordingly, thehydraulic fluid above the piston 34 in the upper portion 38 of chamber32 is forced through the orifices 62 in the piston 34 thereby causingthe desired rebound force. The volume of hydraulic fluid required tofill the lower portion 36 of the working chamber 32 as the piston rod 42moves upward flows from the reservoir 64 into the lower chamber portion36 through the base valve 63.

Accordingly, during the compression stroke, excess hydraulic fluid isforced out of the upper portion 38 of the chamber 32 into the reservoir64 via the flow passage 124, past the annular disk 130 and through theorifice 128 into the upper portion of the reservoir 64. During therebound stroke, hydraulic fluid flows through the base valve 63 into thelower portion 36 of the working chamber 32. In this manner, hydraulicfluid is always cycled in one direction through the reservoir 64, i.e.,from top to bottom. This permits enhanced heat transfer from the fluidthrough the reservoir cylinder 66 to atmosphere to prolong fluid andshock absorber operational life.

Alternative preferred embodiments of the present invention are shown inFIGS. 5 through 8. The following description of these embodimentsutilizes like numbers to describe like parts as in the first embodimentwhere appropriate.

Referring now to FIG. 3 and to the enlarged portion of the shockabsorber 10 shown in FIG. 5, a control valve arrangement according to asecond preferred embodiment of the present invention is shown. Thisembodiment is identical to the embodiment shown in FIG. 4 with theaddition of an annular cup-shaped reservoir 150 around the rod guide 108outside and adjacent to the orifice 128. The reservoir 150 prevents theshock absorber 10 from working into freestroke which can happen incertain conditions. For example, freestroke may occur when air inreservoir 64 flows underneath the valve disk 130. However, freestrokemay be prevented by having a reservoir 150 of hydraulic fluid adjacentto the orifice 128 so as to preclude the entry of air. The reservoir 150comprises a radial portion 152 which joins with the rod guide 108 abovethe end of the pressure tube 30 and an axially extending sleeve portion154 forming an open cup around the sleeve 120.

During the compression stroke, hydraulic fluid passes through theorifice 128 into the reservoir 150, over the top of the sleeve portion154 into the reservoir 64. During the rebound stroke, air is preventedfrom passing through the orifice 128 during any occurrence of freestrokeby the quantity of fluid that builds up and remains in the reservoir150.

Referring now to FIG. 3 and to the enlarged portion of the shockabsorber 10 shown in FIG. 6, a control valve arrangement according to athird preferred embodiment of the present invention is shown. At theupper end of the pressure tube 30 and around the piston rod 42, insideupper end cap 70, is a rubber or plastic annular seal 200. The seal 200prevents dirt and foreign matter from entering the working interior ofthe shock absorber 10. The seal 200 is retained in position by a sealretainer 202 and end cap 70 and forms one side of a first annular cavity204 between the seal retainer 202, the piston rod 42 and the seal 200. Aflow passage 206 is disposed in the seal retainer 202 between theannular cavity 204 and the reservoir 64.

An annular rod guide 208 having an upper section 210 and a lower section212 is positioned around the periphery of the piston rod 42 below theseal retainer 202. The upper section 210 of the annular rod guide 208abuts the seal retainer 202, while the lower section 212 of the rodguide 208 is fitted within the pressure tube 30. The rod guide 208provides radial support to the piston rod 42 thereby allowing axialmovement of piston rod 42 within pressure tube cylinder 30. Positionedbetween the piston rod 42 and rod guide 208 is a plastic sleeve bushing209. The sleeve bushing 209 is used to prevent wear of the rod guide 208and reduces the friction against the piston rod 42.

The upper section 210 of the annular rod guide 208 has an insidediameter greater than the inside diameter of the lower section 212 ofthe rod guide 208 thereby forming a second annular cavity 214 betweenthe piston rod 42, the busing 209, the upper section 210 of the rodguide 208 and the seal retainer 202. A second passage 216 which isdisposed in the seal retainer 202 adjacent to the piston rod 42communicates between the cavity 204 and the cavity 214.

Positioned within annular cavity 214 and around the piston rod 42 is africtional slip ring 218. The frictional slip ring 218 moves betweencontact with the seal retainer 202 when the piston rod 42 moves in anupward direction, and contact with the bushing 209 when the piston rod42 moves in a downward direction. As the piston rod 42 continues upwardor downward travel, the slip ring 218 remains in contact with either theseal retainer 202 or the bushing 209 respectively.

As can be seen in FIG. 6, when the piston rod 42 moves in an upwarddirection during rebound, the slip ring 218 move into contact with theseal retainer 202 thereby sealing off the flow passage 216. Furtherupward movement of the piston rod 42 continues to maintain the slip ring218 in sealing engagement with the seal retainer 202. When piston rod 42is moved downward during compression, the slip ring 218 moves away fromthe seal retainer 202 thus opening the passage 216 from the first cavity204 through the seal retainer 202 to the second cavity 214.

A cylindrical sleeve portion 220 of the seal retainer 202 extendsdownward and is positioned concentric to and radially spaced outwardfrom the upper section 210 of the rod guide 208. The sleeve portion 220is an integral part of the seal retainer 202 and together with the uppersection 210 and the lower section 212 of the rod guide 208 forms a thirdannular cavity 222 in between. An axially aligned third passage 224through the lower section 212 of the rod guide 208 communicates axiallybetween the upper portion 38 of working chamber 32 and the third annularcavity 222. A first orifice 226 through upper section 210 of rod guide208 permits fluid communication between the second cavity 214 and thethird cavity 222.

An annular valve disk 230 positioned on the periphery of the piston rod42 and within the third annular cavity 222 is used to prevent the flowof damping fluid through the flow passage 224. The valve disk 230 isbiased downward against the lower section 212 of the rod guide 208 toclose off the flow passage 224 by a wave washer spring 232 also disposedin third cavity 222. On the upper surface of the lower section 212 ofthe rod guide 208 is a raised valve seat 225. The raised valve seat 225is disposed on the periphery of the flow passage 224 and providespositive seating of valve disk 230 to close off passage 224.

An O-ring 234 disposed above the valve disk 230 within the cavity 22transmits the force from the spring 232 to the annular valve disk 230 soas to bias the valve disk 230 against the valve seat 225. In addition,the O-ring 234 provides a seal between the upper section 210 of the rodguide 208 and the cylindrical sleeve portion 220 of the seal retainer202. Disposed between the wave washer spring 232 and the O-ring 234 is aretaining disk 236. The retaining disk 236 distributes the downwardlydirected spring force from the spring 232 evenly around the O-ring 234.

During the compression stroke of the piston rod 42, the slip ring 218also moves downward with the piston rod 42 away from the seal retainer202 thereby opening second passage 216. Travel of the frictional slipring 218 is terminated when the slip ring 218 contacts the bushing 209on the rod guide 208. As piston rod 42 continues to move in a downwarddirection, the slip ring 218 remains stationary. When the piston rod 42moves in an upward direction, the slip ring 218 frictionally ridesupward on the piston rod 42 until contact with the retainer 202 is made.The slip ring 218 then remains stationary against retainer 202 sealingoff the passage 216 between the cavity 204 and the cavity 214 duringfurther upward motion of the rod 42.

During downward travel of the piston rod 42, the pressure within theworking chamber 32 is higher than the pressure in the reservoir 64. Thepressure of the hydraulic fluid in the working chamber 32 is transmittedthrough the flow passage 224 to the underside of the valve disk 230. Thepressure in reservoir 64, in addition to the spring force generated bythe wave washer spring 232, is felt on the upper side of the O-ring 234.The pressure of the hydraulic fluid in the reservoir 64 is transmittedthrough the reservoir 64, the first passage 206, the first annularcavity 204, through the second passage 216 to the second cavity 214,through the first orifice 226 to the third cavity 222 and the O-ring234. This path allows fluid to flow from the upper side of the O-ring234 and permits the valve disk 230 to lift, compressing the spring 232,and allowing hydraulic fluid to pass through the passage 224, past theseat 225, and into the reservoir 64.

During the rebound stroke, the movement of the piston rod 42 carries theslip ring 218 upward into contact with the seal retainer 202, thusclosing the second flow passage 216. This isolates the path between thereservoir 64 and the upper side of O-ring 234. Therefore, the fluidpressure above the O-ring 234 in the third cavity 222 is at the samepressure as the working chamber 32 beneath the rod guide 208. Due to thefact that the area above the O-ring 234 is greater than the area beneaththe annular disk 230 and due also to the spring force provided by wavewasher spring 232, the annular valve disk 230 is forced against thevalve seat 225 which maintains the flow passage 224 closed. Thus, thehydraulic fluid above the piston 34 in the upper portion 38 of thechamber 32 is forced through the orifices 62 in the piston 34 therebycausing the appropriate rebound force. The hydraulic fluid needed toreplace the hydraulic fluid displaced as the piston rod 42 moves upwardflows from the reservoir chamber 64 into the lower portion 36 throughthe base valve 63.

Thus, during the compression stroke, excess hydraulic fluid is forcedout of the upper portion 38 of the chamber 32 into the reservoir 64 viathe flow passage 224, past the annular valve disk 230 and into the upperportion of the reservoir 64. On the rebound stroke, hydraulic fluidflows through the base valve 63 into the lower portion 36 of the workingchamber 32. In this manner, the hydraulic fluid is again always cycledin one direction through the reservoir 64, i.e., from top to bottom. Asin the previous embodiments, this one-directional flow of hydraulicfluid permits enhanced heat transfer from the fluid through thereservoir tube 66 to atmosphere to prolong fluid and shock absorberoperational life.

Referring now to FIG. 3 and to the enlarged portion of the shockabsorber 10 shown in FIG. 7, a control valve arrangement according to afourth preferred embodiment of the present invention is shown. At theupper end of the pressure tube 30 and adjacent to the periphery of thepiston rod 42 is a rubber or plastic annular seal 400. The seal 400 isdisposed inside the upper end cap 70 and prevents dirt and foreignmatter from entering the working interior of the shock absorber 10.

The seal 400 is retained in position by a seal retainer 402 and an endcap 70 and forms one side of a first annular cavity 404 between a sealretainer 402, the piston rod 42 and the seal 400. To permit fluidcommunication between the annular cavity 404 and the reservoir 64, aflow passage 406 is provided through seal retainer 402.

An annular rod guide 408 having an upper section 410 and a lower section412 is positioned adjacent to the periphery of the piston rod 42 belowthe seal retainer 402. The upper section 410 of the annular rod guide408 abuts the seal retainer 402, while the lower section 412 of the rodguide 408 is fitted within the pressure tube 30. The rod guide 408provides radial support to the piston rod 42 thereby allowing axialmovement of piston rod 42 within the pressure tube cylinder 30. Disposedbetween the piston rod 42 and the rod guide 408 is a plastic sleevebushing 409. The sleeve bushing 409 is used to prevent wear of the rodguide 408 and reduces the friction against the piston rod 42.

The shock absorber 10 also comprises a second annular cavity 414 whichis formed between the piston rod 42, the sleeve bushing 409, the uppersection 410 of the rod guide 408 and the seal retainer 402. A secondpassage 416 through the seal retainer 402 adjacent to the piston rod 42communicates between the cavity 404 and the cavity 414. Positionedwithin the annular cavity 414 and around the piston rod 42 is africtional slip ring 418. The frictional slip ring 418 moves betweencontact with the seal retainer 402 when the piston rod 42 moves in anupward direction, and contact with the sleeve bushing 409 when thepiston rod 42 moves in a downward direction. As the piston rod 42continues upward or downward travel, the slip ring 418 remains incontact with either the seal retainer 402 or the sleeve bushing 409,respectively.

As can be seen in FIG. 7, when the piston rod 42 moves in an upwarddirection, the slip ring 418 moves into contact with the seal retainer402 thereby sealing the flow passage 416 Further upward movement of thepiston rod 42 continues to maintain the slip ring 418 in sealingengagement with the seal retainer 402. When the piston rod 42 is moveddownward, the slip ring 418 moves in a direction away from the sealretainer 402, thus opening the flow passage 416 from the first cavity404 through the seal retainer 402 to the second cavity 414.

A cylindrical sleeve 420 is positioned concentric to and radiallyoutwardly spaced from the upper section 410 of the rod guide 408. Thesleeve 420 is secured between the seal retainer 402 and the lowersection 41 of the rod guide 408 to form a third annular cavity 422. Anaxially aligned third passage 424 through the lower section 412 of therod guide 408 provides fluid communication between the upper portion 38of the working chamber 32 and the third annular cavity 422. A firstorifice 426 through the upper section 410 of the rod guide 408communicates radially between the second cavity 414 and the third cavity422. A second orifice 428 through the sleeve 420 allows fluidcommunication between the third cavity 422 and the reservoir 64.

The shock absorber 10 further comprises an annular valve disk 430positioned about the piston rod 42. The valve disk 430 is disposedwithin the third annular cavity 422 and is used for sealing the passage424. The valve disk 430 is biased downward against an upwardly extendingseat portion 425 of the lower section 412 of the rod guide 408 to closeoff the passage 424 by the helical spring 432 also residing in the thirdcavity 422.

An O-ring 434 disposed above the valve disk 430 within the cavity 422transmits the force from the spring 432 to the annular valve disk 430 toseat the valve disk 430 against the seat portion 425 to close thepassage 424 through the rod guide 408. In addition, the O-ring 434provides a seal between the upper section 410 of rod guide 408 and thecylindrical sleeve 420. Positioned between the helical spring 432 andthe O-ring 434 is a retaining disk 436. The retaining disk 436distributes the downwardly directed spring force from the spring 432evenly around the O-ring 434.

During the compression stroke of the shock absorber, the slip ring 418also moves downward with the piston rod 42 away from the seal retainer402 thereby opening the second passage 416. Travel of the frictionalslip ring 418 is terminated upon the contact with the sleeve bushing409. As the piston rod 42 continues to move downward, the slip ring 418remains stationary. When the piston rod 42 moves upward, the slip ring418 frictionally rides upward on the piston rod 42 until contact withretainer 402 is made. The slip ring 418 then remains stationary againstretainer 402 thereby sealing off passage 416 between cavity 404 andcavity 414 during further upward motion of rod 42.

During downward travel of piston rod 42, there is a higher pressurewithin working chamber 32 than in reservoir 64. Accordingly, thehydraulic fluid is transmitted through the passage 424 to the undersideof the valve disk 430. The hydraulic fluid in reservoir 64 in additionto the spring force is felt on the upper side of the O-ring 434. Thepressure of the hydraulic fluid in the reservoir 64 is transmittedthrough the reservoir 64, the first passage 406, the first annularcavity 404, through the second passage 416 to the second cavity 414,through the first orifice 426 to the third cavity 422 and the O-ring434. This path generates a pressure differential across the O-ring 434and permits the valve disk 430 to lift, compressing the spring 432, andallowing the hydraulic fluid to pass into the reservoir 64 through thesecond orifice 428 in the sleeve 420.

During the rebound, the piston rod 42 is moved in an upward direction.The upward movement carries the slip ring 418 upward into contact withseal retainer 402, thus closing the second passage 416. This isolatesthe path between the reservoir 64 and the upper side of O-ring 434.Therefore, the hydraulic fluid above the O-ring 434 in third cavity 422is at the same pressure as the hydraulic fluid in the working chamber 32beneath the rod guide 408. Due to the fact that the area above theO-ring 434 is greater than the are beneath the annular disk 430 and dueto the spring force provided by the helical spring 432, the annularvalve disk 430 maintains the passage 424 closed, thus preventing flowthrough the orifice 428. Accordingly, the hydraulic fluid above thepiston 34 in upper portion 38 of the chamber 32 is forced through theorifices 62 in the piston 34 causing the appropriate rebound force.

The shock absorber 10 also comprises an annular cup-shaped reservoir 450which is positioned around the rod guide 408 outside and adjacent to theorifice 428. The reservoir 450 prevents the shock absorber 10 fromworking into freestroke which can happen in certain conditions.

The reservoir 450 comprises a radial portion 452 which joins with thelower section 412 at the end of pressure tube 30 and an axiallyextending sleeve portion 454 forming an upwardly open cup around sleeve420. During the compression stroke, hydraulic fluid passes through theorifice 428 into the reservoir 450, over the top of the sleeve portion454 into the reservoir 64. During the rebound stroke, air is preventedfrom passing through the orifice 428 during any occurrence of freestrokeby the fluid quantity that builds up and remains in the reservoir 450.

Thus, during the compression stroke, excess hydraulic fluid is forcedout of the upper portion 36 of the chamber 32 into the reservoir 64 viathe passage 424, past the annular disk 430, through the orifice 428 andthrough the reservoir 450 into the upper portion of the reservoir 64. Onthe rebound stroke, the piston rod volume is replaced by hydraulic fluidflowing through the base valve 63 into lower portion 36. In this manner,hydraulic fluid is once again cycled in one direction through reservoir64, i.e., from top to bottom.

Referring now to FIG. 3 and to the enlarged portion of the shockabsorber 10 shown in FIG. 8, a control valve arrangement according to afifth preferred embodiment of the present invention is shown. Thisembodiment uses fewer parts than those previously described. At theupper end of the pressure tube 30 and adjacent to the periphery of thepiston rod 42, inside upper end cap 70, a rubber or plastic annular seal500 is produced. The seal 500 is disposed inside the upper end cap 70and prevents dirt and foreign matter from entering the working interiorof the shock absorber 10. The seal 500 is retained in position by a sealretainer 502 and the end cap 70 and forms one side of a first annularcavity 504 between the seal retainer 502, the piston rod 42 and the seal500. A flow passage 506 is disposed between the annular cavity 504 andthe reservoir 64 in the seal retainer 502. The seal retainer 502 has adownwardly extending sleeve portion forming a rod guide 508 disposedadjacent to the periphery of the piston rod 42. The seal retainer 50 isfitted into the pressure tube 30. The rod guide 508 provides radialsupport to the piston rod 42 allowing axial movement of the piston rod42 within pressure tube 30.

Positioned between the piston rod 42 and the rod guide 508 is a plasticsleeve bushing 509. The sleeve bushing 509 prevents wear of the rodguide 508 and reduces the friction against rod 42. The upper end of thebushing 509, the piston rod 42, and the seal retainer 502 form a secondcavity 514. A second flow passage 516 in the seal retainer 502 adjacentpiston rod 42 allows fluid communication between the cavity 504 and thecavity 514.

Positioned within the annular cavity 514 and around the piston rod 42 isa frictional slip ring 518. The slip ring 518 moves between contact withthe seal retainer 502 when piston rod 42 moves in an upward direction,and contact with the sleeve bushing 509 when the piston rod 42 moves ina downward direction. As the piston rod 42 continues upward or downwardtravel, the slip ring 518 remains in contact with either the sealretainer 502 or the sleeve bushing 509, respectively.

As can be seen in FIG. 8, when the piston rod 42 moves in an upwarddirection, the slip ring 518 moves into contact with seal retainer 502thereby sealing off the passage 516. Further upward movement of thepiston rod 42 continues to maintain the slip ring 518 in sealingengagement with the seal retainer 502. When piston rod 42 is moveddownward, the slip ring 518 moves in a direction away from the sealretainer 502 thus opening the passage 516 from the first cavity 504through the seal retainer 502 to the second cavity 514

The pressure cylinder 30 and the rod guide 508 form a third cavity 520therebetween. Disposed within the cavity 520 is a teflon valve sleeve522 having a bore 523 therethrough. Disposed in the rod guide 508between the cavity 520 and the cavity 514 is passage 525. The pressurecylinder 30 has an orifice 524 through its upper end adjacent and inalignment with a radial bore 526 in rod guide 508. An axially alignedbore 528 in the rod guide 508 communicates between the bore 526 and theupper portion 38 of working chamber 32. The rod guide 508 is spacedradially inward from the pressure cylinder 30 by a narrow annular gap530 which the valve sleeve 522 closes. The valve sleeve 522 is retainedwithin the cavity 520 by contact with the annular shoulder 532 on thelower outer end of the rod guide 508. The valve sleeve 522 is biaseddownward against shoulder 532 by a helical coil spring 534 which isdisposed within cavity 520.

Operation of this embodiment is similar to the other embodiments exceptthat during the compression stroke, the valve sleeve 522 is pushedupward against spring pressure exerted by the spring 534 until the bore523 is aligned with the orifice 524 and the bore 526 so as to pass fluidfrom the chamber 32 through the bore 528, the bore 526, the bore 523,and the orifice 524 into the reservoir 64.

As in the other embodiments shown and above described, during therebound stroke, the passage 516 is sealed by the slip ring 518 andtherefore the bore 526 remains sealed. Thus, once again hydraulic fluidis cycled in only one direction through the reservoir 64. Thisembodiment, however, utilizes only 6 components to form the controlvalve. It is simpler to construct and is more economical than thecomparable embodiment shown in FIG. 7 which has 9 components comprisingthe control valve.

Referring now to FIG. 9, a control valve arrangement according to thesixth preferred embodiment cf the present invention is shown. At theupper end of the pressure tube 30 and adjacent to the periphery of thepiston rod 42, a rubber or plastic annular seal 600 is provided. Theseal 600 is disposed inside the upper end cap portion 70 of thereservoir tube 66 and prevents dirt and foreign matter from entering theworking interior of the shock absorber 10. The seal 600 is retained inposition by a seal retainer 602 and the end cap portion 70.

The shock absorber 10 includes three annular cavities 604, 606 and 608.The first annular cavity 604 is disposed between the seal retainer 602,the piston rod 42 and the seal 600. The second annular cavity 606 isformed between the piston rod 42 and the seal retainer 602 by means of aradially displaced surface region of the seal retainer 602. Finally, thethird annular cavity 608 is formed by an annular groove located on thelower surface 610 of the seal retainer 602.

To allow the first annular cavity 604 to fluidly communicate with theannular fluid reservoir 64, the shock absorber 10 further has a firstflow passage 612 and a second flow passage 614. The first flow passage612 extends upwardly from the annular fluid reservoir 64 between thereservoir tube 66 and the seal retainer 602. The second flow passage 614extends radially outward and angularly downward in the seal retainer 602from the first annular cavity 604 to the first flow passage 612.

To allow the second and third annular cavities 606 and 608 to fluidlycommunicate with the first annular cavity 604, the shock absorber 10 hasthird and fourth flow passages 616 and 618. The third flow passage 616extends between the first annular cavity 604 and the second annularcavity 606 and is disposed between the piston rod 42 and the sealretainer 602. The fourth flow passage 618 extends radially outward anddownwardly in the seal retainer 602 from the second annular cavity 606to the third annular cavity 608.

To control the flow of damping fluid through the third flow passage 616,an annular seal 620 is provided. The annular seal 620 is slidablydisposed on the piston rod 42 in the second annular cavity 606. When thepiston rod 42 is moving in an upward direction during rebound, theannular seal 620 moves upward until the seal interferes with the sealretainer 602 and prevents further upward movement of the annular seal620. When the annular seal 620 interferes with the seal retainer 602,the annular seal 620 prevents damping fluid from flowing through thethird flow passage 616. When the piston rod 42 is moving in a downwarddirection, the annular seal 620 also moves in a downward direction untilthe annular seal 620 interferes with a sleeve bushing described belowwhich is secured to the rod guide 622. Because the annular seal 620 isdisplaced from the third flow passage 616 upon downward movement of thepiston rod 42, the pressure of the damping fluid contained in theannular fluid reservoir 64 is allowed to fluidly communicate with thethird flow passage 616.

The shock absorber 10 further comprises a sleeve bushing 624 which isdisposed between the piston rod 42 and the rod guide 622. The sleevebushing 624 is secured to the rod guide 622 and allows for verticalmovement of the piston rod 42. Because the sleeve bushing 624 reducesthe friction associated with movement of the piston rod 42, the sleevebushing 624 is able to reduce wear of the piston rod 42 which wouldotherwise occur.

To allow damping fluid to flow between the upper portion of the workingchamber 32 and the annular fluid reservoir 64, the shock absorber 10further comprises a fifth flow passage 626 and a sixth flow passage 628.The fifth flow passage 626 extends vertically upward in the annular rodguide 622 from the annular fluid reservoir 64, while the sixth flowpassage 628 extends upward in the annular rod guide 622 from the upperportion of the working chamber 32.

To control the flow of damping fluid between the fifth and sixth flowpassages 626 and 628, a deflectable valve member 630 is provided. Thevalve member 630, defining a membrane, is disposed between the sealretainer 602 and the rod guide 622 so as to prevent the flow of dampingfluid between the third annular cavity 608 and the fifth and sixth flowpassages 626 and 628. The membrane 630 is made of a suitable materialwhich can be deformed when the pressure of damping fluid flowing throughthe fifth and sixth flow passages 626 and 628 is greater than thepressure of damping fluid in the third annular cavity 608. While themembrane 630 may be made from rubber, it is to be understood that othersuitable materials may be used.

To filter the damping fluid flowing through the reservoir tube 66 andthe pressure cylinder 30, a filter 632 is provided. The filter 632 isdisposed between the reservoir tube 66 and the pressure cylinder 30.Since the damping fluid in the annular fluid reservoir 64 passes throughthe reservoir tube 66 in one direction, the damping fluid will flowthrough the filter 632 which removes impurities which may otherwiseeventually interfere with the operation of the shock absorber 10. Thefilter 632 is made from a material, or composition of materials havingthe desired permeability characteristic and which is compatible withhydraulic fluid.

The operation of the shock absorber 10 shown in FIG. 9 will now bedescribed. During compression, the seal 620 moves in a downwarddirection so as to allow damping fluid to flow through the third flowpassage 616. Damping fluid is therefore able to flow from the annularfluid reservoir 64 to the third annular cavity 608 by means of the firstflow passage 612, the second flow passage 614, the first annular cavity604, the third flow passage 616, the second annular cavity 606 and thefourth flow passage 618. Accordingly, the pressure inside the thirdannular cavity 608 is substantially equal to the pressure of the dampingfluid within the annular fluid reservoir 64 during compression.

Since during compression the pressure of damping fluid in the upperportion of the working chamber 32 is greater than the pressure of thedamping fluid in the annular fluid reservoir 64, the membrane 630 flexesin an upward direction due to the pressure differential between thedamping fluid in the third annular cavity 608 and the damping fluid inthe upper portion of the working chamber 32. Because the membrane 630flexes in this manner, damping fluid is able to flow from the upperportion of the working chamber 32 to the annular fluid reservoir 64through the fifth flow passage 626 and the sixth flow passage 628.

During rebound of the shock absorber 10 when the piston rod 42 is movingin an upward direction, the annular seal 620 is displaced upwardly untilthe annular seal 620 interferes with the seal retainer 602. When theannular seal 620 interferes with the seal retainer 602, the seal 620prevents damping fluid from flowing through the third flow passage 616.Accordingly, the pressure of damping fluid within the third annularcavity 608 remains substantially the same pressure as the damping fluidin the annular fluid reservoir 64 when upward movement of the piston rod42 began. Because the working area of the membrane 630 which is exposedto damping fluid in the third annular cavity 608 is greater than theworking area exposed to the damping fluid in the sixth flow passage 628,the membrane 630 does not flex even though the pressure of the dampingfluid in the upper portion of the working chamber 32 may be greater thanthe damping fluid in the third annular cavity 608. Because the membrane630 does not flex, the membrane 630 is able to prevent the flow ofdamping fluid between the upper portion of the working chamber 32 andthe annular fluid reservoir 64 through the fifth and sixth flow passages626 and 628. Accordingly, the damping fluid which enters the workingchamber 32 from the annular fluid reservoir 64 during rebound only flowsthrough the base valve (not shown).

Because the membrane 630 allows damping fluid to flow from the upperportion of the working chamber 32 into the annular fluid reservoir 64through the fifth and sixth flow passages 626 and 628 duringcompression, yet prevents damping fluid from flowing from the upperportion of the working chamber 32 to the annular fluid reservoir 64during rebound, damping fluid flows primarily in a downward directionthrough the reservoir tube 66 during operation of the shock absorber 10.Because the damping fluid moves in primarily one direction through thereservoir tube 66, the filter 632 is able to remove impurities whichwould otherwise interfere with the operation of the shock absorber 10.In addition, because the flow of damping fluid moves primarily in onedirection through the reservoir tube 66, the shock absorber 10 is ableto dissipate a greater amount of heat than would otherwise be possible.

Referring now to FIG. 10, a control valve arrangement according to theseventh preferred embodiment of the present invention is shown. At theupper end of the pressure tube 30 and adjacent to the periphery of thepiston rod 42, a rubber or plastic annular seal 700 is provided. Theseal 700 is disposed inside the upper end cap 70 within the reservoirtube 66 and prevents dirt and foreign matter from entering the workinginterior of the shock absorber 10. The seal 700 is retained in positionby a seal retainer 702 and the end cap 70.

The shock absorber 10 includes three annular cavities 704, 706 and 708.The first annular cavity 704 is disposed between the seal retainer 702,the piston rod 42 and the seal 700. The second annular cavity 706 isformed between the piston rod 42, the seal retainer 702 and the valvehousing 710 by means of radially displaced surface regions of the valvehousing 710. Finally, the third annular cavity 708 is formed by anannular groove located on the lower surface 712 of the valve housing710.

To allow the first annular cavity 704 to fluidly communicate with theannular fluid reservoir 64, the shock absorber 10 further has a firstflow passage 714. The first flow passage 714 extends upwardly from theannular fluid reservoir 64 between the end cap 70 and the rod guide,716, valve housing 710 and seal retainer 702.

To allow the second and third annular cavities 706 and 708 to fluidlycommunicate with the first annular cavity 704, the shock absorber 10 hassecond and third flow passages 718 and 720. The second flow passage 718extends between the first annular cavity 704 and the second annularcavity 706 and is disposed between the piston rod 42 and the sealretainer 702. The third flow passage 720 extends downwardly in the valvehousing 710 from the second annular cavity 706 to the third annularcavity 708.

To allow the second annular cavity 706 to fluidly communicate with theupper portion 38 of working chamber 32, the shock absorber 10 furtherhas a fourth flow passage 722. The fourth flow passage 722 extendsupwardly from the working chamber 32 between the piston rod 42 and theinside diameter of a sleeve bushing 724 and the valve housing 710.

To control the flow of damping fluid through the second flow passage718, an annular seal 726 is provided. The annular seal 726 is slidablydisposed on the piston rod 42 in the second annular cavity 706. When thepiston rod 42 is moving in an upward direction during rebound, theannular seal 726 moves upward until the seal interferes with the sealretainer 702 and prevents further upward movement of the annular seal726. When the annular seal 726 interferes with the seal retainer 702,the annular seal 726 prevents damping fluid from flowing through thesecond flow passage 718. When the piston rod 42 is moving in a downwarddirection, the annular seal 726 also moves in a downward direction untilthe annular seal 726 interferes with the valve housing 710. Because theannular seal 726 is displaced from the second flow passage 718 upondownward movement of the piston rod 42, the pressure of the dampingfluid contained in reservoir 64 is allowed to fluidly communicate withthe third annular cavity 708 via third flow passage 720, second annularcavity 706, second flow passage 718, first annular cavity 704 and firstflow passage 714.

The shock absorber 10 includes a sleeve bushing 724 which is disposedbetween the piston rod 42 and the rod guide 716. The sleeve bushing 724is secured to the rod guide 716 and allows for vertical movement of thepiston rod 42. Because the sleeve bushing 724 reduces the frictionassociated with movement of the piston rod 42, the sleeve bushing 724 isable to reduce wear of the piston rod 42 which would otherwise occur.

To allow damping fluid to flow between the upper portion of the workingchamber 32 and the annular fluid reservoir 64, the shock absorber 10further comprises a fifth flow passage 728 and a sixth flow passage 730.The fifth flow passage 728 extends vertically upward in the annular rodguide 716 from the working chamber 32, while the sixth flow passage 730extends downwardly from the top surface of the annular rod guide 716 andfluidly communicates with an inwardly extending bore 732 provided at theouter periphery of rod guide 716. Bore 732 fluidly communicates withfirst flow passage 714 so as to permit flow between working chamber 32and the annular fluid reservoir 64.

To control the flow of damping fluid between the fifth and sixth flowpassages 728 and 730, a flexible valve member 734 is provided. The valvemember 734 is disposed within the third annular cavity 708 so a tocontrol the flow of damping fluid between the third annular cavity 708and the fifth and sixth flow passages 728 and 730. The flexible valvemember 734 is made of a suitable material which can be compliantlydeformed when the pressure of damping fluid flowing through the fifthand sixth flow passages 728 and 730 is greater than the pressure ofdamping fluid in the third annular cavity 708. The valve member 734preferably is fabricated from rubber and includes a metallic disc member735 integrally associated therewith to provide additional stability andstiffness.

The operation of the shock absorber 10 shown in FIG. 10 will now bedescribed. During compression, the seal 726 moves in a downwarddirection so as to prevent damping fluid from flowing through the fourthflow passage 722 and into the second annular cavity 706. The pressure ofthe damping fluid is therefore able to fluidly communicate from theannular fluid reservoir 64 to the third annular cavity 708 by means ofthe first flow passage 714, the first annular cavity 704, the secondflow passage 718, the second annular cavity 706 and the third flowpassage 720. Accordingly, the pressure inside the third annular cavity708 is substantially equal to the pressure of the damping fluid withinthe annular fluid reservoir 64 during compression.

Since during compression the pressure of damping fluid in the upperportion of the working chamber 32 is greater than the pressure of thedamping fluid in the annular fluid reservoir 64, the valve member 734flexes in an upward direction due to the pressure differential betweenthe damping fluid in the third annular cavity 708 and the damping fluidin the upper portion of the working chamber 32. Because the valve member734 flexes in this manner, damping fluid is able to flow from the upperportion of the working chamber 32 to the annular fluid reservoir 64through the fifth flow passage 728, the sixth flow passage 730 and firstflow passage 714.

During rebound of the shock absorber 10 when the piston rod 42 is movingin an upward direction, the annular seal 726 is displaced upwardly untilthe annular seal 726 interferes with the seal retainer 702. When theannular seal 726 interferes with the seal retainer 702, the seal 726prevents damping fluid from flowing through the second flow passage 718.Additionally, when the annular seal 726 is in this position, fluid ispermitted to flow from working chamber 32 through fourth flow passage722, second annular cavity 706 and third flow passage 720 into thirdannular cavity 708. Accordingly, the pressure of damping fluid withinthe third annular cavity 708 remains substantially the same pressure asthe damping fluid in the working chamber 32 when upward movement of thepiston rod 42 began. Because the working area of the valve member 734which is exposed to damping fluid in the third annular cavity 708 isgreater than the working area exposed to the damping fluid in the fifthflow passage 728, the valve member 734 does not flex. Because the valvemember 734 does not flex, the valve member 734 is able to prevent theflow of damping fluid between the upper portion of the working chamber32 and the annular fluid reservoir 64 through the fifth and sixth flowpassages 728 and 730. Accordingly, the damping fluid which enters theworking chamber 32 from the annular fluid reservoir 64 during reboundonly flows through the base valve (not shown).

Because the valve member 734 allows damping fluid to flow from the upperportion of the working chamber 32 into the annular fluid reservoir 64through the fifth and sixth flow passages 728 and 730 duringcompression, yet prevents damping fluid from flowing from the upperportion of the working chamber 32 to the annular fluid reservoir 64during rebound, damping fluid flows primarily in a downward directionthrough the reservoir tube 66 during operation of the shock absorber 10.Because the flow of damping fluid moves primarily in one directionthrough the reservoir tube 66, the shock absorber 10 is able todissipate a greater amount of heat than would otherwise be possible.

Referring now to FIGS. 11 and 12, a control valve arrangement accordingto the eighth preferred embodiment of the present invention is shown.The eighth preferred embodiment of the present invention is similar tothat of the seventh preferred embodiment. However, the rod guide 716further has a plurality of flow passages 736, as well as a plurality ofslots 738. The flow passage 736 extends axially from the sixth flowpassage 730 to the slots 738. The slots 738 are semi-elliptical in shapeand are disposed on the lower radially outward surface of the rod guide716 immediately above the pressure cylinder tube.

To reduce aeration of the damping fluid flowing through the flowpassages 736, a rubber sleeve 744 is provided. The rubber sleeve 744extends circumferentially around the pressure cylinder 30 and extendsdownwardly from the rod guide 716 to a position approximately one inchbelow the level of damping fluid stored in the annular fluid reservoir64. A flow passage 746 is formed between the radially outward surface ofthe pressure cylinder 30 and the radially inward surface of the rubbersleeve 744 so as to permit damping fluid from the sixth flow passage 730to flow to the annular fluid reservoir 36 through the flow passage 736as well as the flow passage 746. By allowing damping fluid to flow inthis manner, aeration of the damping fluid flowing into the annularfluid reservoir 64 is reduced. Furthermore, because the sleeve 744 isformed from rubber, the sleeve 744 can expand to increase the size ofthe flow passage 746 when the shock absorber 10 is damping extremeshock.

To secure the rubber sleeve 744 against the rod guide 716, an annularcrimp ring 748 is provided. The annular crimp ring 748 is disposed onthe radially outer periphery of the rubber sleeve 744 at its uppersurface. Because the crimp ring 748 exerts a compressive force againstthe rubber sleeve 744, the crimp ring 748 is able to secure the rubbersleeve 744 against the rod guide 716.

It is apparent that the preferred embodiments illustrated and describedabove are well calculated to fill the objects stated. For example,damping fluid is not required to flow through the base valve duringcompression so that damping during compression may be substantiallyfully controlled by the piston. Accordingly, the present invention maybe used in conjunction with adjustable damping suspension systems toincrease the range of damping such systems can provide. It will beappreciated, however, that the present invention is susceptible tomodification, variation and change. For example, the present inventionmay be used for shock absorbers which dampen the movement of truck cabs,seats and other articles. It is therefore to be understood that withinthe scope of the appended claims, the invention may be practicedotherwise than as specifically described.

What is claimed is:
 1. A shock absorber comprising:a pressure tubesymmetrically disposed about an axis, said pressure tube forming aworking chamber having upper and lower portions; a reservoir tube forstoring hydraulic fluid, said reservoir tube disposed concentric to andradially extended from said pressure tube; a flexible valve memberoperable from controlling the flow of hydraulic fluid between said upperportion of said working chamber and said reservoir tube; and secondvalve means for allowing flow of said hydraulic fluid from saidreservoir tube into said lower portion of said working chamber and forpreventing flow of said fluid from said lower portion of said workingchamber into said reservoir tube; a piston slidably disposed between andseparating said upper and lower portions of said working chamber, saidpiston allowing restricted flow of hydraulic fluid between said upperand lower portions of said working chamber; an elongated piston rodhaving first and second ends, said first end being attached to saidpiston, said second end of said elongated piston rod extending along theaxis of said pressure tube through said upper portion of said workingchamber and out one end of said pressure tube; a rod guide disposedbetween said piston rod and said pressure tube; a valve housing disposedconcentrically about said piston rod and adjacent said rod guide; afirst annular seal disposed around said piston rod; an annular sealretainer disposed concentrically about said piston rod and adjacent tosaid valve housing; a first annular cavity disposed between said pistonrod, said first annular seal, and said seal retainer; a second annularcavity disposed between said piston rod, said valve housing and saidannular seal retainer; a third annular cavity disposed between saidvalve housing and said rod guide; passage means for communicating withsaid reservoir tube, first annular cavity, said second annular cavity,said third annular cavity, said upper portion of said working chamberand said valve member; and a second annular seal disposed in said secondannular cavity, said second annual seal operably to restrict movement ofsaid flexible valve member during rebound of said shock absorber bycontrolling the flow of damping fluid between said third annular cavityand said reservoir tube.
 2. The shock absorber according to claim 1further comprising:a rod guide disposed between said piston rod and saidpressure tube; a valve housing disposed concentrically about said pistonrod and adjacent said rod guide; a first annular seal disposed aroundsaid piston rod; an annular seal retainer disposed concentrically aboutsaid piston rod and adjacent to said valve housing; a first annularcavity disposed between said piston rod, said first annular seal, andsaid seal retainer; a second annular cavity disposed between said pistonrod, said valve housing and said annular seal retainer; a third annularcavity disposed between said valve housing and said rod guide; saidpassage means comprising a first flow passage communicating with saidreservoir tube; a second flow passage communicating with said firstannular cavity and said second annular cavity; a third flow passagecommunicating with said second annular cavity and said third annularcavity; a fourth flow passage communicating with said upper portion ofsaid working chamber; a fifth flow passage communicating with the upperportion of said working chamber and said valve member; a sixth flowpassage communicating with said reservoir tube and said valve member;and a second annular seal disposed in said second annular cavity, saidsecond annular seal operably to restrict movement of said flexible valvemember during rebound of said shock absorber by controlling the flow ofdamping fluid between said third annular cavity and said reservoir tube.3. The shock absorber according to claim 2 wherein said flexible valvemember is disposed within said third annular cavity, said third annularcavity defined by an annular groove located on a lower surface of saidvalve housing, and wherein said flexible valve member is defined as anannular seal acting to control the flow of damping fluid between saidfifth and sixth flow passages such that said valve member is deflectablydeformed when the pressure of damping fluid acting in said fifth flowpassage is greater than the fluid pressure in said third annular cavity.4. The shock absorber according to claim 1, further comprising means forreducing aeration of damping fluid comprising a rubber sleeve disposedbetween said pressure tube and said reservoir tube.